CODEWITHSUNDEEP
pythonregexpython-3.x
corvid
corvid

Reputation: 11187

match a representation of a number with regex

I am trying to find a regular expression which could be used to scan if a string is a number.

There are some examples here:

>>> expressions = [ 
  "3",
  "13.",
  ".328",
  "41.16",
  "+45.80",
  "+0",
  "-01",
  "-14.4",
  "1e12",
  "+1.4e6",
  "-2.e+7",
  "01E-06",
  "0.2E-20"
]

How can one capture all of these examples in a regular expression?

Upvotes: 0

Views: 98

Answers (2)

Sven
Sven

Reputation: 2889

You can use [-+]?[0-9]*\.?[0-9]*([eE][-+]?[0-9]+)?' to match numbers, but the solution @Cyber proposed is much better.

def filterPick(lines, regex):
    matches = map(re.compile(regex).match, lines)
    return [m.group() for m in matches if m]

print filterPick(expressions, '[-+]?[0-9]*\.?[0-9]*([eE][-+]?[0-9]+)?')

>>>['3', '13', '.328', '41.16', '+45.80', '+0', '-01', '-14.4', '1e12', '+1.4e6', '-20', '01E-06', '0.2E-20', '3']

Upvotes: 1

Cory Kramer
Cory Kramer

Reputation: 117856

This seems like a try/except block might be better in this situation

expressions = [
  "3",
  "13.",
  ".328",
  "41.16",
  "+45.80",
  "+0",
  "-01",
  "-14.4",
  "1e12",
  "+1.4e6",
  "-2.e+7",
  "01E-06",
  "0.2E-20",
  "word",
  "3ad34db"
]

for value in expressions:
    try:
        num = float(value)
        print('{} is a number'.format(num))
    except ValueError:
        print('{} is not a number'.format(value))

Output

3.0 is a number
13.0 is a number
0.328 is a number
41.16 is a number
45.8 is a number
0.0 is a number
-1.0 is a number
-14.4 is a number
1000000000000.0 is a number
1400000.0 is a number
-20000000.0 is a number
1e-06 is a number
2e-21 is a number
word is not a number
3ad34db is not a number

Upvotes: 2

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